Aquatic fouling organisms such as barnacles, tubeworms, common mussels, Bugula neritina, sea squirts, green laver, sea lettuce, and slimes attach to ships (especially ship bottoms), fishing tools such as fishing nets and fishing net accessories, and structures submerged in seawater such as power plant aqueducts, leading to dysfunction, impaired appearance, and other problems of the ships and so on.
Since a conventional organic tin-containing copolymer has been banned, triorganosilyl group-containing copolymers which have low toxicity and are environment-friendly have been developed, and have been used for antifouling coating materials (Patent Literature 1).
When the triorganosilyl ester-containing copolymer is used, the copolymer initially dissolves in seawater at a constant rate. The dissolving rate of the coating film gradually increases, and becomes excessively high after a long period of time has elapsed. Unfortunately, this makes the design of the coating material difficult. Because of the above, disclosed is an antifouling coating material that exerts the long-term stable dissolution of the coating film by using rosin, a rosin derivative, or a metal salt thereof in addition to the triorganosilyl ester-containing copolymer (Patent Literature 2).
Although the antifouling coating material can exert the long-term stable dissolution of the coating film, the coating film after long-term soaking in seawater tends to cause coating film defects such as a crack. In order to provide a solution to these problems, various proposals have been presented, including blending the triorganosilyl ester-containing copolymer with an additional resin, a plasticizer, other various additives, etc.
Although the additional resin-blended antifouling coating material has improved coating film properties regarding a crack, etc., to some degree, the material cannot achieve the long-term stable dissolution of the coating film any more (Patent Literatures 3 to 6). In addition, when a small amount of the plasticizer is added, the plasticizer-blended antifouling coating material hardly exerts an advantageous effect. By contrast, when a large amount of the plasticizer is added, the coating film properties regarding a crack, etc., are improved to some degree. Unfortunately, the coating film is fragile and the dissolution of the coating film becomes too large. Further, the antifouling coating material blended with fiber as another additive can produce an effect of preventing a coating film defect such as a crack. Unfortunately, the dissolution of the coating film is decreased such that the long-term stable dissolution of the coating film cannot be achieved (Patent Literature 7).
So far, there is no antifouling coating composition which can keep the antifouling performance and stable dissolution of the coating film without causing coating film defects such as a crack during long-term seawater treatment.